Includes abstract. / Includes bibliographical references (p. 116-137). / The work outlined in this thesis aimed to further our understanding of jasmonate signalling by identifying specific promoter elements and associated transcription factors important for gene regulation by methyl jasmonate. A cDNA encoding a β-glucosidase, PYK10, was previously isolated using the differential display technique in an attempt to isolate methyl jasmonate-induced genes in Arabidopsis thaliana. β-glucosidases catalyse the breakdown of glucosinolates into glucose and sulphate releasing toxic by-products which play a role in plant defence against insects and pathogens.

Includes abstract. / Includes bibliographical references. / A better understanding of how this commercially important seaweed responds at a genetic level to stresses faced in the aquaculture environment would not only be advantageous to the South African industry, but this knowledge is essential for selecting and/or engineering macroalgal strains that are either more tolerant or resistant to these stresses. This requires in vivo analysis of G. gracilis gene function and regulation in order to introduce new or improved genes into G. gracilis, and for this to be possible, a protocol for transformation of recombinant DNA into G. gracilis is required. In this study a transformation and tissue culture system for G. gracilis was developed. These tools provide the necessary groundwork for future genetic manipulation studies that are essential for improving our understanding of the role that various genes play in stress response and tolerance in G. gracilis.

Includes abstract. / Includes bibliographical references (leaves 172-191). / Has accompanying material on CD. / The resurrection plant, Xerophyta humilis is used as a model system to identify and characterise genes which play an important role in conferring desiccation tolerance in plants. In this study, the expression of a novel gene named desiccation induced-1 (dsi-1VOC) during desiccation in X. humilis and desiccationsensitive plants is characterised.

Includes bibliographical references. / Cancer is the second leading cause of death among both men and women and accounts for 13% of total deaths worldwide. Enormous efforts have therefore been made to cope with this problem, but unfortunately limited success has been achieved with most of the current therapeutic strategies. The T-box family of developmentally important transcription factors plays a role in the genesis of cancer and shows much promise as a focus for targeted therapeutic approaches to treat cancer. For example, the T-box factor TBX3 is overexpressed in a number of cancers including breast cancer but the mechanism(s) responsible for this upregulation as well as the precise role of TBX3 in the progression of this disease still need to be elucidated. This study provides novel data that show that TBX3 is specifically involved in breast cancer cell proliferation and migration and that its upregulation by the TGF-β1 signalling pathway mediates the TGF-β1-regulated anti-proliferative and pro-migratory effects. Furthermore, this study demonstrates that TBX3 mediates the anti-proliferative function of TGF-β1 through repressing transcription of its homologue, TBX2, which allows for the de-repression of p21 and a G1 cell cycle arrest. The findings of the current study are of great significance as it identifies TBX3 as a potential target for the development of novel breast cancer therapeutics. In order to ascertain the function of upregulated expression of TBX3, cell culture models were established in which TBX3 was either (1) stably silenced in an invasive breast ductal carcinoma cell line (MCF-7) which was previously shown to overexpress TBX3 or (2) overexpressed in a normal human breast epithelial cell line (MCF-12A). The resultant cells were then compared to control cells and tested for key characteristics of cancer. The data generated provide evidence that increased TBX3 levels inhibit breast epithelial cell proliferation in growth curve, BrdU incorporation and MTT assays. However, in vitro motility assays show that TBX3 may contribute to breast cancer progression by enhancing the migratory ability of these cells.

Includes abstract. / Includes bibliographical references (p. 119-132).

Includes abstract. / Includes bibliographical references (leaves 125-145). / This dissertation aims to examine allele-specific splicing in human and mouse using publicly available datasets. Such datasets, which have been generated from multiple tissue sources and from individuals of diverse backgrounds, are rich and cheap reservoirs of transcript isoforms resulting from alternative splicing as well as isoforms resulting from mutations or polymorphisms (allele-specific isoforms). Published tools were used to analyse microarray and genomic data. However, for the assessment of allele-specific splicing using publicly available high-throughput transcript sequences, we present two novel methods: a heuristic method for quantifying the prevalence of allele-specific splicing and a more sophisticated maximum likelihood method for the detection of individual examples of allele-specific splicing. These methods make use of transcripts that can be mapped to both polymorphisms and computationally predicted mRNA isoforms. Inference of polymorphic alleles from transcripts is laborious hence a pre-computed database was created for the human data and made publicly available for use by the wider research community.

Includes bibliographical references (leaves 199-253). / This study attempted to characterize at a transcriptional level, the defence responses of Arabidopsis thaliana after infection by Botrytis cinerea, using microarrays. The first microarray experiment focused on profiling Arabidopsis genes induced by B. cinerea over time (temporal) while the second investigated spatial expression of Arabidopsis genes from the point of inoculation. A number of genes were up- and down-regulated specifically at 12 hrs, others at 24 hrs while others were up- and down-regulated at both time points. Similarly, some genes were specifically induced very close to the lesion while others in more distal tissue.

To our knowledge, this study represents the first analysis of gene expression using cDNA microarrays in the red macroalga G. gracilis. Western hybridization analysis was used to establish whether the observed changes in gene expression following exposure to disease elicitors positively correlated to changes at the protein level.

Includes abstract. / Includes bibliographical references. / Ever since the discovery of a cellulolytic actinomycete inside the gut of a termite, there has been considerable interest in the metabolic abilities and the diversity of these bacteria within this complex environment. However, until fairly recently, most investigations of termite hindguts involved the higher termites from the Termitidae family. Little attention was paid to the lower termites, and even less to the family Hodotermitidae. The main aim of this project was to explore the actinobacterial diversity of the paunch and colon hindgut regions of one particular member of the family Hodotermitidae, Microhodotermes viator. No previous work of this nature has ever been attempted on this particular termite species.

Includes bibliographical references (leaves 103-111).